Ferroelectric BaTiO₃ Freestanding Sheets for an Ultra-High-Speed Light-Driven Actuator

Light-driven actuators convert optical energy into physical motion. Organic materials, commonly used in light-driven actuators thus far, suffer from two limitations: slow repetitive operation and the requirement of two different light sources. Herein, we report a high-speed, light-driven actuator that can be operated by a single light source with low-energy density. We achieved this breakthrough by utilizing a freestanding epitaxial sheet of ferroelectric BaTiO₃. One repetitive operation takes only 120 μs, which is 10⁴ times faster than that of organic-based counterparts. The high-speed operation is derived from the light-induced nonthermal deformation provided by the excellent ferroelectricity (remnant polarization of 23 μC/cm²) and piezoelectricity (d₃₃ of 600 pm/V) of the sheet. The displacement-to-length ratio is achieved to be 3.7% with a relatively low laser power density (10-200 mW/cm²) compared to previously reports (150-10⁹ mW/cm²). Furthermore, the actuator was operable even in water, demonstrating its potential in various applications.